The present invention relates to sealed ball bearings, and more particularly to a sealed ball bearing for supporting various rotary parts while incorporated into such equipment as computer devices and audio-visual devices.
A small ball bearing called a miniature bearing or an extra-small bearing is used for supporting a rotary part such as a capstan or the like of, e.g., an audio-vidual device. The ball bearing includes, as shown in FIG. 9, an inner race 2 having an inner raceway track 1 on an outer surface thereof; an outer race 4 having an outer raceway track 3 on an inner surface thereof and being arranged so as to be concentric with the inner race 2; and a plurality of balls 5 arranged so that the balls can roll easily between the inner raceway track 1 and the outer raceway track 3. The respective balls 5 are held by a cage 9 so as to be rollable.
At two positions of both edge portions on the inner surface of the outer race 4 are holding grooves 6, which are formed so as to extend over the circumference. An annular seal plates 7 are supported by the respective holding grooves 6. Each of the seal plates 7 includes: a reinforcing member 10 made of a plate material having sufficient rigidity such as stainless steel; and an elastic member 11 made of a material such as rubber or synesthetic resin. Both the inner and the outer circumferential end portions of the elastic member 11 are projected from both the inner and the outer circumferential end portions of the reinforcing plate 10, and support the seal plates 7 by both inner edge portions of the outer race 4 by engaging the outer circumferential projections with the holding grooves 6. Under this condition, the inner circumferential end portions of the elastic member 11 slidably contact with both edge portions on the outer surface of the inner race 2.
To attach the seal plates to the surface of the outer race or the inner race, the holding groove 6 and the circumferential end portion of the elastic member 11 are formed into predetermined shapes, and therefore the circumferential end portion is engaged with the holding groove 6 with sufficient strength, as disclosed in, e.g., Unexamined Japanese Utility Model Publication No. Sho. 49-140548. That is, as shown in FIG. 10, a circumferential end portion 12 of the elastic member 11 bonded onto the seal plate 7 can be freely pressed into the holding groove 6 by elastically deforming the circumferential end portion 12.
Moreover, the thus shaped seal plate 15 is formed by punching a plate blank that is formed by coating the elastic member 18 on a single surface of a metal plate forming the reinforcing plate 17 into an annular form as disclosed in Unexamined Japanese Patent Publication No. Sho. 54-132045.
However, to facilitate the attachment of the circumferential end portion 12 of the seal plate 7 to the holding groove 6 as well as to make the attached seal plate 7 hard to come off, the above-described conventional structure requires strict dimensional accuracy in forming the circumferential end portion 12 and the holding groove 6, thus making the sealed ball bearings costly.
To overcome this problem, a large width is required for the holding groove 6. Consequently, if the volume of a space 8 (FIG. 9) in which the balls 5 are arranged is to be reserved, the width of the sealed ball bearing must be increased. If such width is fixed, the volume of the space 8 becomes small. The reduction in the volume of the space 8 means, however, a reduction in the amount of grease to be charged into such space, which leads to a shortened life of the ball bearing.